Several investigators reported the close association of hypertension and tubulointerstitial changes in patients with primary membranous nephropathy [1,2]. Recently, we suggested that active treatment with corticoste-roid is beneficial for patients with primary membranous nephropathy [3]. However, it is difficult to determine whether only tubulointerstitial changes are correlated with the prognosis in such patients. We attempted to determine the relationship between the tubulointerstitial changes and the levels of urinary protein or serum creatinine (s-Cr) at the time of renal biopsy and the final follow-up in 19 patients with primary membranous nephropathy not associated with hypertension. Light-and electron-microscopic examinations and immunofluorescence were performed on renal biopsy specimens as described previously [3]. All patients were divided into three groups, i.e., mild, moderate and advanced stages, according to semiquantitative scoring of the tubulointerstitial lesions detected by light microscopy. The observation periods varied from 30 to 122 months (mean 72). Levels of urinary protein and s-Cr were measured at the time of renal biopsy and final follow-up in our outpatient clinic. The levels of urinary protein in the mild